In a Ge optical receiver which uses Ge in a light absorbing layer, a structure wherein a cap layer comprising SiGe or Si is formed on a Ge layer for covering the Ge layer has been known. In the structure, it is possible to reduce dark current of the Ge optical receiver by forming a Schottky barrier between the SiGe or Si cap layer and a metal electrode. An SiGe cap layer can be deposited in a satisfactory manner on a Ge layer, which is formed by selective epitaxial growth and comprises facet surfaces, by optimizing conditions of deposition; thus, it provides stable effect for reducing dark current. On the other hand, since a difference between a lattice constant of an Si cap layer and that of Ge is large, it is difficult to deposit the layer in a satisfactory manner on a facet surface of a Ge layer, especially. Thus, in a Ge optical receiver in which an Si cap layer is used, although it is possible to reduce dark current when a low bias voltage is applied, it is reported that there is a problem that dark current increases when a high bias voltage is applied.